SIMFEROPOL, Ukraine, Feb 26 (Reuters) - Thousands of pro-Russia separatists tussled with supporters of Ukraine's new leaders in Crimea on Wednesday as tempers boiled over the future of the region following the upheaval that swept away President Viktor Yanukovich.

One person died, apparently of a heart attack, and two others were trampled and injured when people stumbled and fell to the ground in the crush, witnesses said.

About 2,000 people, many of them ethnic Tatars who are the indigenous group on the Black Sea peninsula, converged on the parliament building to support the 'Euro-Maidan' movement which overturned Yanukovich in Kiev after three months of protests.

They were met by a similar number of pro-Russia demonstrators who bellowed loyalty to Moscow and denounced the "bandits" who had seized power in the Ukrainian capital.

The two sides, who were held apart by police, rallied noisily outside the parliament which, under pressure from pro-Russia forces, had called an emergency session for later on Wednesday to discuss the crisis.

Crimea was transferred from Russia to Ukraine in 1954 in the Soviet-era by then Soviet leader Nikita Khrushchev. With a part of Russia's Black Sea fleet based in the port of Sevastopol, it is the only region of Ukraine where ethnic Russians dominate in numbers, although many ethnic Ukrainians in other eastern areas speak Russian as their first language.

With Crimea now the last big bastion of opposition to the new post-Yanukovich political order in Kiev, Ukraine's new leaders are voicing alarm over signs of separatism there.

The Tatar demonstrators had apparently feared parliament might make some decision altering the status of the region, while the separatists, many of them ethnic Russians, are opposing the 'EuroMaidan' protests which they see as hostile to Russia's interests.

Ethnic Tatars, who accounted for most of the pro-Maidan demonstrators, rallied under a pale-blue flag, shouting: "Ukraine! Ukraine!" and the Maidan's refrain of "down with the gang!"

The pro-Russian crowds, some of them cossacks in silk and lambswool hats, shouted back "Crimea is Russian!".

More pro-Russia loyalists were brought in by bus from other parts of the peninsula and soon outnumbered the crowds of Tatars and 'EuroMaidan' supporters. They began playing Russian songs and religious choral music from amplifiers set up in the portico of a church.

Tension over Crimea is likely to escalate further on Wednesday after President Vladimir Putin put Russian troops on high alert for a drill. Since Yanukovich's downfall, all eyes have been on Putin, who in 2008 ordered an invasion of Georgia to protect self-declared independent regions with many ethnic Russians, which he then recognised as independent states.

Rudik Asmanov, a 42-year-old Tatar businessman, said: "We need to show our support for Kiev, to honour 'Heaven's Hundred'," he said, referring to casualties on the protesters' side in Kiev.

Alexei, 17, part of the pro-Russia crowd, who was wearing a bandana over his face and carrying a baseball bat in a backpack, said: "The Tatars are our enemy now. They're siding with the bandits in Kiev. We need to defend ourselves or it will be chaos."

The Tatars, a Turkic ethnic group, were victimised by Soviet dictator Josef Stalin in World War Two and deported en masse to Soviet Central Asia in 1944 on suspicion of collaborating with Nazi Germany.

Tens of thousands of them returned to their homeland after Ukraine gained independence with the collapse of the Soviet Union at the end of 1991.

Tatar leader Refat Chubarov, who came to address the crowd but was shouted down by pro-Russians supporters, told Reuters: "We have a long memory of what the Russians did to us Tatars.

"We are now a minority in our own homeland because of them ... We have fought alongside the Ukrainians more often than against them - our loyalty is with them," he said.

Most of the crowd dispersed as it grew dark though a few hundred people were still on the square near the parliament building, mostly ethnic Russians gathered in small groups holding Russian flags. (Writing by Richard Balmforth; Editing by Giles Elgood)